A conventional cable system arrangement is depicted in FIG. 1. In such a system, the cable operator processes audio/video (A/V) content 14 with conditional access (CA) technology from manufacturer A (system A) using CA encryption equipment 18 compliant with system A at the cable system-headend 22. The encrypted A/V content along with system information (SI) 26 and program specific information (PSI) 27 is multiplexed together and transmitted over the cable network 32 to a user's Set-top box (STB) or other receiver 36. STB 36 incorporates decrypting CA equipment from system A (manufacturer A) 40 that decrypts the A/V content. The decrypted A/V content can then be supplied to a television set 44 for viewing by the user.
In a cable system such as that of FIG. 1, digital program streams are broken into packets for transmission. Packets for each component of a program (video, audio, auxiliary data, etc.) are tagged with a packet identifier or PID. These packet streams for each component of all programs carried within a channel are aggregated into one composite stream. Additional packets are also included to provide decryption keys and other overhead information. Otherwise unused bandwidth is filled with null packets.
Since the encryption process defined by conditional access system A is proprietary to the manufacturer of the STB 36, it is difficult and expensive for a cable operator to utilize alternative sources for this hardware. Consequently, the cable or satellite operator may be locked in to a particular supplier for hardware.
The above-referenced commonly owned patent applications, and others, address this issue and therein describe inventions relating to various aspects of methods generally referred to herein as partial encryption or selective encryption. More particularly, systems are described therein wherein selected portions of a particular selection of digital content are encrypted using two (or more) encryption techniques while other portions of the content are left unencrypted. By properly selecting the portions to be encrypted, the content can effectively be encrypted for use under multiple decryption systems without the necessity of encryption of the entire selection of content. In some embodiments, only a few percent of data overhead is needed to effectively encrypt the content using multiple encryption systems. This results in a cable or satellite system being able to utilize Set-top boxes (STB) or other implementations of conditional access (CA) receivers from multiple manufacturers in a single system—thus freeing the cable or satellite company to competitively shop for providers of Set-top boxes.
In each of these disclosures, the content is carried in the clear using a primary Packet Identifier (PID). A secondary PID (or shadow PID) is also assigned to the program content. Selected portions of the content are then encrypted under two (or more) encryption systems and the encrypted content transmitted using both the primary and secondary PIDs (one PID or set of PIDs for each encryption system). The so-called legacy STBs operate in a normal manner decrypting encrypted packets arriving under the primary PID and ignoring secondary PIDs. The newer (non-legacy) STBs operate by associating both the primary and secondary PIDs with a single program. Packets with a primary PID are decoded normally and packets with a secondary PID are first decrypted then decoded. The packets associated with both PIDs are then assembled together to make up a single program stream. Certain embodiments consistent with the present invention address a mechanism for conveying the PIDs to the non-legacy STBs in a manner that does not disrupt the operation of legacy STBs or otherwise violate rules generally used for transmission of digital video signals to the legacy STBs.